In this study, waste corrugated paper was used as carbon precursor with KOH-NaOH mixture (mole ratio was 51:49 and the melting point is 170 °C) as activator to prepare porous carbon at different reaction temperature and different mass ratio of KOH-NaOH mixture/waste corrugate paper fiber. The micro-morphology, pore structure information and composition of porous carbon were analyzed, and the formation mechanism of pores was investigated. The effect of activator amount and pyrolysis temperature on the morphology and structure of porous carbon were studied. The adsorption capacity of porous carbon was evaluated with the methylene blue as model pollutant. The effect of adsorbent amount, adsorption time and temperature on the adsorption performance of the porous carbon were analyzed. The maximum specific surface area is 1493.30 m2 ·g−1 and the maximum adsorption capacity of methylene blue is 518 mg·g−1. This study provides a new idea for efficient conversion and utilization of waste paper.